1. Technical Field of the Invention
The present invention relates to an original transfer apparatus for automatically transferring an original to and discharging an original from a platen section of a copying apparatus, an image reading apparatus, a microfilm photographing apparatus or the like in which an image is exposed, read or photographed, and particularly to an original transfer apparatus provided with a transfer belt stretched between a pair of rollers so as to be opposed to the platen, and a suitable number of back-up rollers provided inside of the transfer belt and adapted to press the transfer belt in pressure contact with the platen section.
2. Description of the Related Arts
In such a kind of conventional apparatus, as a transfer means for transferring an original to and discharging an original from a platen section, usually a white belt is used. Therefore, after being used for a long time, sometimes the transfer belt becomes too soiled to be cleaned by a cleaner and a read-out image becomes also soiled. Accordingly, the transfer belt is exchanged with a new one at predetermined times.
An art for easily exchanging a transfer belt is disclosed in Japanese Unexamined Utility Model Publication No. 62-25484. In this art, supporting holes for supporting a pair of rollers around which a transfer belt is stretched are provided in a frame of a device, and each of the holes is provided with an outwardly opened cut off portion, so that a shaft of each roller is inserted through the cut off portion into the supporting hole, and by fitting the shaft into a bearing and then fitting the bearing into the supporting hole.
Further, apparatus are known in which bearing portions for supporting a pair of rollers are detached from a frame of the apparatus by removing a cover, or in which after removing a cover, a front side plate constituting a frame is detached and then a transfer belt is forwardly pulled out.
Further, an apparatus is known in which a pair of rollers with a transfer belt stretched therearound, back-up rollers and the like are set into a frame of a belt unit, and this belt unit is adapted to be attachable to and detachable from a frame of the device.
However, in the construction disclosed in the Japanese Unexamined Utility Model Publication, a cover covering the frame of the apparatus including the bearing portions has to be preliminarily moved away in order to detach the bearings for exchanging the transfer belt, so that troublesome operations are required. Further, other devices in which the transfer belt is detached after moving the cover away have the same disadvantage.
Further, in a construction in which a belt unit is attached to and detached from the frame of the device, a frame of the belt unit has to be provided in addition to the frame of the original transfer device, so that the apparatus becomes disadvantageously expensive.
Further, as shown in FIG. 1, a back-up roller a is formed of a rotation shaft b with a plurality of small rollers c fixed thereon and disposed inside of a transfer belt d. This back-up roller a is supported at the rotation shaft b thereof by a holder f fixed to a frame e for supporting the transfer belt d, and adapted to press the transfer belt d against a platen glass g by its own weight or the like. Thereby, the transfer belt d is in pressure contact with the platen glass g at some positions in the longitudinal direction to provide a transfer force, whereby a delivered original can be pulled on the platen glass g so as to be copied and discharged from the platen glass g.
However, as shown in FIG. 1, a conventional holder is fitted to the frame such that an end thereof protrudes near the edge portion of the transfer belt d, and attention must be paid to ensure that the holder can sufficiently bear the rotation shaft b and at the same time prevent the end of the holder from interfering with the edge portion of the transfer belt d.
However, since the transfer belt d is hardly supported by the back-up roller a, when it is driven, the end portion of the transfer belt d shakes between two supporting rollers h as shown in solid and imaginary lines. As a result, the end portion of the transfer belt d is apt to be in contact with an end face of the holder. Therefore, the transfer belt is apt to be worn out and damaged, and the life thereof becomes shortened.
Such a shaking of the end portion of the transfer belt d remarkably occurs when the transfer belt d is driven both in the positive and negative directions, and further, when the transfer belt g moves in zigzag direction the trouble is also serious.